The invention relates to an adjusting device for adjusting a camshaft relative to a camshaft gear wheel driven by a crankshaft, wherein parts provided for the adjustment procedure are arranged on the camshaft gear wheel and on the camshaft.
Among other things, stepper motors, which enable self-locking and an exact, but merely discrete, i.e., non-continuous, adjustment, can be used as adjusting devices. Furthermore, for achieving self-locking and a high gear reduction, a worm gear pair can be used. However, for a relatively large amount of friction, worm gear pairs exhibit low efficiency and require materials that are resistant to wear and heat.
DE 195 08 328 A1 presents a self-locking adjusting device for rotating two bracing parts relative to each other. One of the two bracing parts comprises internal gearing, into which locking bars or teeth can be inserted in a straight-line radial direction. The teeth are guided in chambers between webs of the other bracing part, such that the radially inwards and outwards movement is precisely enabled. The teeth are supported inwards on a control surface, which is formed as an outer surface of an egg-shaped control element. When the control element rotates, the teeth are thus periodically pushed outwards in the radial direction, wherein a few of the teeth engage in the teeth gaps. The outer end sections of the teeth and the recesses or teeth gaps of the internal gearing taper outwards, so that the teeth transfer torque between the webs of the second bracing part and the internal gearing of the first bracing part for eccentric insertion into a recess.
However, a disadvantage in this adjusting device is first that only partial self-locking is achieved. When torque acts upon the bracing part with internal gearing, only the one or two teeth, which are pressed against the eccentric region of the control element by the teeth of the internal gearing, contribute to the self-locking effect, depending on the engagement situation of the teeth. The opposing teeth likewise contribute minimally to the self-locking, like those teeth, which are in the radially outer position, i.e., positive-fit in the recess, and those teeth, which are in the radially inner position, i.e., not engaged in the teeth gaps of the internal gearing. However, the possibly only one tooth, which is to contribute to the self-locking effect, can transfer a force not directed towards the rotational axis from the internal gearing to the control element between the point of application of the internal gearing at its outer contact surface and its inner contact surface contacting the control element, which thus leads to transmission of torque. In this way, especially for the use of only a few teeth, no positive-fit connection between the internal gearing and the webs and thus, at least for an unfavorable engagement situation of the teeth, also no complete self-locking can be achieved.
Furthermore, a play-free configuration of such an adjusting device is problematic. The teeth that can move linearly in the radial direction slide with their side surfaces on the side surfaces of the webs of the second bracing part. However, a play-free arrangement of the teeth between the webs is practically impossible; for achieving a low-friction guidance of the teeth between the webs, a certain overdimension is necessary. Finally, due to the manufacturing-specific tolerances, play between the control surface and the tooth remains even in the positive-fit engagement of a tooth in its radially outer position in a recess of the internal gearing.
Camshaft adjusters are used especially for engine speed-dependent and load-dependent adaptation of the valve opening and closing times for an internal-combustion engine in order to improve the filling. The camshaft is driven by the crankshaft, e.g., by means of toothed belts, a roller chain, or spur pinions, on a camshaft gear wheel, to which the camshaft is connected. The camshaft adjustment is realized by rotating the camshaft relative to the camshaft gear wheel, wherein the transfer of torque must also be guaranteed during the adjustment. Therefore, adjusting devices with high, continuous adjustment accuracy and reliable self-locking are required in all situations. For this purpose, in conventional camshaft adjusting devices, a control piston adjusts against a spring force in a flanged shaft connected to the camshaft through, e.g., a hydraulic drive, wherein the flanged shafts are connected to the camshaft gear wheel and, if necessary a positioning piston, by means of oblique gearing. However, such a configuration is complicated, expensive, and subject to maintenance. Furthermore, complicated feed lines from a central hydraulic pump are required in the vehicle.